Pressure venting instrument casing assembly

ABSTRACT

An instrument casing assembly for pressure gauges and the like providing controlled venting to atmosphere in the event of internal overpressure buildup. A cylindrical cup-shaped window or crystal representing the front side is received axially interfitting within the open face of a cup-shaped casing representing the rear side. Axially positioned between opposing surfaces of the window and casing is a resilient gasket by which a seal can be effected thereat. For maintaining the seal there is provided an annular collar ring resiliently biasing the window and casing axially toward each other and against the gasket. In the event of an internal overpressure buildup, increasing pressure acting against the inside window surface forces separation thereof from the gasket in opposition to the biasing force of the collar.

United States Patent [191 Luich Mar. 5, 1974 PRESSURE VENTING INSTRUMENTCASING ASSEMBLY Ronald Joseph Luich, Bridgeport, Conn.

[73] Assignee: Dresser Industries, Inc., Dallas, Tex. [22] Filed: Jan.23, 1973 [21] Appl. N0.: 325,986

[75] Inventor:

[52] US. Cl. 73/431, 73/416 Primary ExaminerDonald O. Wo'odiel Zitorney,Agent, or Firm-Daniel Rubin 57 ABSTRACT An instrument casing assemblyfor pressure gauges and the like providing controlled venting toatmosphere in the event of internal overpressure buildup. A cylindricalcup-shaped window or crystal representing the front side is receivedaxially inter-fitting within the open face of a cup-shaped casingrepresenting the rear side. Axially positioned between opposing surfacesof the window and casing is a resilient gasket by which a seal can beeffected thereat. For maintaining the seal there is provided an annularcollar ring resiliently biasing the window and casing axially towardeach other and against the gasket. lnthe event of an internaloverpressure buildup, increasing pressure acting against the insidewindow surface forces separation thereof from the gasket in oppositionto the biasing force of the collar.

10 Claims, 4 Drawing Figures PRESSURE VENTHNG INSTRUMENT (IASIINGASEMBLY BACKGROUND OF THE INVENTION 1. The field of art to which theinvention pertains includes the art of instrument casing constructionsadapted for venting of internal overpressure.

2. Instruments for the measuring and/or controlling of space conditionssuch as temperature or pressure are commonly subject to wide variationsof internal pressures as the function of the system conditions to whichit is intended to respond. Typically, a pressure gauge employs a Bourdontube operably movable in response to pressure changes and in whichinternal pressure received from the system being sensed is normallycontained. Should the Bourdon tube incur inservice failure in the formof a pressure leak, system pressure intended to be contained can quicklyfill and even explode the case or crystal. Since such a possibilityrepresents a safety hazard to equipment and personnel in the area, it iscommon to provide a form of venting to prevent buildup and avoid flyingfragments from an explosion which could otherwise result. Ventingstructures of various forms for gauge cases and the like are well knownand are in wide commercial use as exemplified by U.S. Pat. Nos.2,833,149; 3,298,557; 3,388,601; 3,434,330 and 3,630,089.

Because of the wide and extensive commercial use of such instruments,they are marketed by many manufacturers with a high order of pricecompetition. Consequently, each gauge manufacturer constantly strivesfor minimal product cost frequently achieved by designs and productiontechniques which result in substantial savings in labor and/ormaterials. While venting structures of the aforementioned patents havethemselves functioned well for the instruments for which they have beenemployed, cost reduction in the venting structure itself or an improvedvent structure designed to accommodate in otherwise cost-reducedinstruments, can contribute substantially to the commercial success ofthe article of which it is a part. At the same time, a minimal standardof quality and operability is dictated by the frequent need for approvalfrom Underwriters Laboratories prior to marketing.

Most recently, in order for their approval to be granted, UnderwritersLaboratories has imposed increasingly severe test criteria as comparedto previous such tests. A consequence of this change has been to rendermany existing venting structures currently unsuitable for variousreasons, including required dimensional stability at highertemperatures. At the higher temperatures on the order of 250F.,frequently employed plastic compositions such as cellulose acetatebutyrate are deleteriously affected and therefore become unsuitable.Contra, thermoplastics such as polycarbonate otherwise having hightemperature stability are also characterized by greater strength andless flexibility on which prior constructions relied rendering themgenerally unsuitable in former constructions for meeting currentstandards.

SUMMARY OF THE INVENTION The invention relates to a novel instrumentcasing assembly providing for venting of internal overpressure. Morespecifically, the invention relates to an instru ment casing assemblyhaving a highly effective vent structure employable in mass produced,small diameter gauges on the order of l-inch face diameters of a typecommonly used in association with fire extinguishers. Not only does thecasing assembly in accordance herewith economically achieve the desiredventing feature, but its structure'is at the same time characterized byphysical properties able to meet current standards of UnderwritersLaboratories.

It is therefore an object of the invention to provide a novel andimproved casing assembly capable of venting internal overpressure fromwithin the casing.

It is a further object of the invention to provide a novel and improvedventing structure for a gauge assembly otherwise constructed as awaterproof and dustproof enclosure.

It is a further object of the invention to effect the aforementionedobjects with casing components at least partially of generallyinflexible thermoplastic composition characterized by relatively hightemperature dimensional stability as compared to thermoplasticscompositions similarly employed for these purposes in the prior art.

It is a still further object of the invention to provide a novel ventingstructure for an instrument casing as in the last mentioned object thatis highly effective yet capable of use with small gauge diameters atvery minimal production cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. ii is a front face view of apressure gauge instrument constructed in accordance herewith;

FIG. 2 is a side elevation partially in section;

FIG. 3 is an enlarged fragmentary view of the encircled portion of FIG.2 in its normal unventing relation; and

FIG. 4 is an enlarged fragmentary view of the encircled portion of FIG.2 during its pressure venting relation.

Referring now to the drawings, the casing assembly in accordanceherewith includes a transparent crystal or window 10 fomied as agenerally cylindrical cupshaped molded unit of relatively hightemperature thermoplastic such as polycarbonate having dimensionalstability at temperatures to on the order of at least 250F. Comprisingthe unitary structure of crystal 10 is front face Ill merging integrallywith annular side wall 12 which terminates rearwardly in a radialserrated flange 13. Beneath the crystal, there is defined a generallyopen cavity 14 while peripherally about front face 1 1 there is defineda radial flat 15 for reasons as will be described.

For receiving crystal 10 in an axial interfit therewith, there isincluded a cup-shaped, shell-like case 18 of a relatively thin gaugemetal such as stainless steel. Comprising case B8, is a generallyradially concave back wall l9 merging into an annular flat forming thebackside of radial ledge 20. Radially beyond ledge 20 the case bendsaxially to its termination at 21 to define an open face closelysurrounding received end flange 13 of crystal 10 whereby the crystal andcase together cooperate for generally enclosing the working componentsof the instrument.

As here shown, the working components may, by way of example, be that ofa pressure gauge intended to be responsive to variations of pressureconditions being sensed. For those purposes, there is provided a Bourdontube 24 within the casing secured between crystal and a dial plate 25received in an annular central recess 28 so as to be visible through thecrystal from the front of the instrument. The dial plate includesgraduations 26 with which a pointer 27 attached to the Bourdon tubecooperates to indicate values of pressure received at the instrument.Pressures to be sensed thereby are received through an open end 30 ofBourdon tube 24 secured in a bore 31 of a socket 32. The socket in turnis centrally secured in rear wall 19 and is threaded at 33 for mountinginto a threaded well suitably provided in the system in which it is tobe installed.

To effect the seal and vent structure in accordance herewith, an annularresilient gasket 36 of suitable resilient composition such as rubber orthe like is positioned intervening between case ledge 20 and serratedflange 13 of crystal l0. Securing the components generally dusttight andwatertight in the latter relation is achieved by means of an annularcollar ring 37 biasing the crystal and casing axially toward each otherand oppositely against gasket 36. Collar ring 37 is of metal such asstainless steel sufficiently thin to afford it a spring-like resilience.In order to function in the manner hereof the ring is shaped by bendingor crimping into a U-channel configuration to form an annular side wall38 merging with axially opposite radial flanges 39 and 40 in the frontand rear, respectively. It is to be noted that flange 39 has a slightlygreater radial extent than does flange 40.

For supporting the collar ring tensioned in its assem bled biasingrelation, the terminal end of flange 39 is adapted to seat againstcrystal flat while flange 40 is received behind case wall 19 againstradial surface 44. The extent of bending or crimping of ring 37 issufficient for flanges 39 and 40 when engaging the crystal and casing toplace the collar in tension urging them together in a relativelydustproof, waterproof relation about gasket 36. In the event ofoverpressure incurred within the assembly, a pressure buildup in cavity14 increasingly acts against the inside surface of crystal face 11urging the crystal away from gasket 36 in opposition to the axialbiasing force being exerted by collar 37. On sufficient buildup ofinternal pressure to on the order of 5-90 psig., crystal l0 graduallydisplaces from gasket 36 in the manner best illustrated in FIG. 4 todefine a gap 50 through which overpressure can escape about the crystalpast ring flange 39. So long as the latter situation exists, pressurefrom within continues to be relieved as shown by the arrows in FIG. 4.When venting is completed, the inherent biasing force imposed by flange39 restores the crystal to its former relation with gasket 36immediately restoring the original water and dusttight seal relation ofthe components.

In operation, a gauge assembly as hereinbefore described is inserted ina system in which pressure is to be sensed. Under normal conditions ofservice, the casing assembly will provide a dust and watertightconstruction so as to maintain the internal working components clean andfree of moisture. On an excess pressure being encountered within thecasing, pressure acting axially against the inside surface of crystalface 11 causes the crystal to displace from the gasket enabling therequired venting to occur.

From the above description there is disclosed an instrument casingassembly providing a novel safety construction for the venting ofinternal overpressure by combination of simple but effective featureswhich lends itself to high volume production at minimum production cost.Not only, by virtue of simplicity with a minimum quantity of components,is the construction hereof regarded to be relatively inexpensive toproduce 5 as compared to similar purpose constructions of the prior art,but at the same time it lends itself to extremely small gauge design onthe order of 1-inch and less that are normally difficult to manufacture.At the same time, a most important attribute is its compliance with therelatively more difficult criteria associated with standards recentlyimposed by Underwriters Laboratories.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the drawings and specification shall be interpreted asillustrative and not in a limiting sense.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An instrument casing assembly comprising in combination:

a. a unitary generally cup-shaped transparent crystal having a radiallyextending front face integrally merging with an annular side wall;

b. a cup-shaped, shell-like case having a radially extending back wallintegrally merging with an annular side wall defining an open face inwhich to at least partially receive the side wall of said crystal in aperipherally surrounding axial interfit therewith;

c. an annular resilient gasket positioned intervening between the endface of said crystal side wall and an internal radial surface portion ofsaid case back wall thereat; and d. a generally resilient U-shapedannular collar ring axially extending to centrally surround said crystaland case in a tension relation therewith, said ring having axiallyspaced radial flanges one of which engages said crystal and the other ofwhich engages said case to bias said case and crystal axially towardeach other into sealing engagement with said gasket in the absence ofinternal overpressure while permitting axial displacement of said caseand crystal for releasing said sealing engagement in the presence of asufficient internal overpressure. 2. An instrument casing assemblyaccording to claim I in which said collar ring is operative forreleasing said sealing engagement in response to internal overpressureacting internally against the front face of said crystal at a magnitudesufficient to overcome the biasing force of said ring.

3. An instrument casing assembly according to claim 2 in which saidcollar ring is comprised of relatively thin metal stock capable ofexerting a predetermined biasing force against said crystal and case.

4. An instrument casing assembly according to claim 3 in which saidcrystal is comprised of a relatively rigid thermoplastic compositionhaving dimensional stability to at least 250F.

5. An instrument casing assembly according to claim 4 in which theplastic composition of said crystal comprises polycarbonate.

radial length than said other ring flange.

9. An instrument casing assembly according to claim 8 including a dialplate centrally positioned in said case at least partially interveningbetween said gasket and case back wall thereat.

10. An instrument casing assembly according to claim 9 in which theplastic composition of said crystal comprises polycarbonatev

1. An instrument casing assembly comprising in combination: a. a unitarygenerally cup-shaped transparent crystal having a radially extendingfront face integrally merging with an annular side wall; b. acup-shaped, shell-like case having a radially extending back wallintegrally merging with an annular side wall defining an open face inwhich to at least partially receive the side wall of said crystal in aperipherally surrounding axial interfit therewith; c. an annularresilient gasket positioned intervening between the end face of saidcrystal side wall and an internal radial surface portion of said caseback wall thereat; and d. a generally resilient U-shaped annular collarring axially extending to centrally surround said crystal and case in atension relation therewith, said ring having axially spaced radialflanges one of which engages said crystal and the other of which engagessaid case to bias said case and crystal axially toward each other intosealing engagement with said gasket in the absence of internaloverpressure while permitting axial displacement of said case andcrystal for releasing said sealing engagement in the presence of asufficient internal overpressure.
 2. An instrument casing assemblyaccording to claim 1 in which said collar ring is operative forreleasing said sealing engagement in response to internal overpressureacting internally against the front face of said crystal at a magnitudesufficient to overcome the biasing force of said ring.
 3. An instrumentcasing assembly according to claim 2 in which said collar ring iscomprised of relatively thin metal stock capable of exerting apredetermined biasing force against said crystal and case.
 4. Aninstrument casing assembly according to claim 3 in which said crystal iscomprised of a relatively rigid thermoplastic composition havingdimensional stability to at least 250*F.
 5. An instrument casingassembly according to claim 4 in which the plastic composition of saidcrystal comprises polycarbonate.
 6. An instrument casing assemblyaccording to claim 4 in which the terminal end face of said crystaladapted to engage said gasket includes a serrated texture.
 7. Aninstrument casing assembly according to claim 4 in which said frontcrystal face includes an annular recessed flat defined at the nearperiphery surface thereof for receiving said one ring flange.
 8. Aninstrument casing assembly according to claim 7 in which said one ringflange is of relatively greater radial length than said other ringflange.
 9. An instrument casing assembly according to claim 8 includinga dial plate centrally positioned in said case at least partiallyintervening between said gasket and case back wall thereat.
 10. Aninstrument casing assembly according to claim 9 in which the plasticcomposition of said crystal comprises polycarbonate.